Palletized cargo is transported in military aircraft. Sometimes the cargo is transferred from one airport to another. In other instances the cargo may be air dropped by parachute to a remote site.
In an air drop sequence the pallet is restrained laterally by a guide rail on either side and in the longitudinal direction of aircraft flight by load sensitive latches. The latches release when the force of the extraction parachute, attached to the pallet, exceeds a predetermined triggering load level in the latches. The release load level may be adjusted for pallet weight, number of latches engaged, parachute size, and aircraft speed. The load level at which the pallet is released is critical because it ensures that the parachute is fully deployed and will extract the load properly.
A major problem in prior art extracting systems involved a so-called zipper affect. This phenomenon was present when multiple latches restrained a single pallet. When the latches did not engage the pallet evenly and the parachute extraction load was applied differentially to some of these latches, the latches would then release in sequence rather than at a single instant. When that happened, the force to extract the pallet was unpredictable and substantially less than the sum of the restraint force of all the latches. In this instance, when the pallet left the aircraft the parachute might not be fully deployed and the cargo could tumble. If the pallet tumbles it could entangle the recovery chute and the cargo could be lost.
The desired sequence occurs when the parachute is deployed, the extraction force builds to a desired level and all the latches release simultaneously.